The following description relates to one or more improved optical pickup devices configured to perform read/write operations with a common objective lens for optical disks complying with three different standards such as a CD, DVD, and HD DVD having a higher recording density than that of the DVD.
An optical pickup device configured to perform read/write operations with a common objective lens for two or more optical disks complying with respective different standards is disclosed, for example, in Japanese Patent Provisional Publications No. HEI 9-306024 (see FIG. 1, hereinafter referred to as '024 Publication), No. 2004-79146 (see paragraphs 0312 and 0313, hereinafter referred to as '146 Publication), and No. 2006-147126 (see FIG. 1 and paragraphs 0031 to 0034, and 0047, hereinafter referred to as '126 Publication). The '024 Publication discloses an optical system that employs a common objective lens for a CD and DVD and changes magnification of the objective lens depending on sorts of optical disks in order to restrain aberration due to temperature change. Particularly, the optical system is configured to cause converged light to be incident onto the objective lens in use of the DVD and to cause collimated light to be incident onto the objective lens in use of the CD.
The '146 Publication discloses a technique to correct spherical aberration due to wavelength change or temperature change with a refractive index distribution changing device in a device that performs read/write operations with a common objective lens for optical disks such as the CD, DVD, and an optical disk having a higher recording density than that of the DVD with blue laser light. The refractive index distribution changing device is configured with a liquid crystal layer provided between a pair of transparent electrodes facing each other, at least one of which is divided into a plurality of concentric sections. When a voltage is applied to a part of the concentric sections, an orientation condition of liquid crystal molecules in the liquid crystal layer is electrically controlled to change a refractive index distribution in the liquid crystal layer.
Additionally, the '126 Publication discloses, as a first embodiment, an optical pickup capable of read/write operations with a common optical system for the CD, DVD, and HD DVD. The optical system is configured to correct aberration due to wavelength difference in use of the DVD and HD DVD with an objective lens having a step-shaped annular zone structure formed thereon, and to correct spherical aberration that cannot completely be corrected by the objective lens with a phase compensator in use of the CD. There is employed as the phase compensator, a liquid crystal aberration correcting device configured in the same manner as disclosed in the '146 Publication.
However, the optical pickup described in the '024 Publication can meet only two types of optical disks, the DVD and CD, yet is not adopted to meet three types of optical disks which also include the HD DVD having a higher recording density than that of the DVD.
Additionally, the '146 Publication discloses that the liquid crystal device is employed in order to correct the spherical aberration due to the temperature change in use of the HD DVD. However, as far as the '146 Publication discloses, since the DVD especially has a great absolute value of magnification, it might result in an increased aberration due to a tracking operation and thus an undesired trouble in the read/write operations.
Further, the optical pickup disclosed in the '126 Publication renders collimated light incident onto the objective lens in use of any of the CD, DVD, and HD DVD, and therefore the aberration is not increased by the tracking operation. However, since an aberration amount to be corrected by the phase compensator in use of the CD is significant, it is required to thicken the liquid crystal device employed as the phase compensator and to ensure a high relative positional accuracy between the objective lens and phase compensator. The phase compensator is driven along with the objective lens by a tracking mechanism, and therefore a thick liquid crystal results in a heavier load on the tracking mechanism, and thus a more difficult assembling process is required to ensure the high relative positional accuracy between the objective lens and phase compensator. Additionally, the '126 Publication does not disclose a technique to restrain aberration due to environmental change such as temperature change in use of the DVD and HD DVD.